1. Field of the Invention
The present invention relates to a node redundancy method, an interface card, an interface device, a node device, and a packet ring network system used in networks.
2. Description of the Related Art
Recently, there has been a remarkable increase in data traffics over the Internet mainly based on the Ethernet (Registered trade name) or IP (Internet Protocol) packets, rapid increase in ADSL (Asymmetric Digital Subscriber Line) users, and advent of VoIP (Voice over IP) technique. As a result, a network of packet rings (described as a packet ring network or simply, as a ring hereinafter), in which packets are directly processed on the ring network for band management for each packet or for statistic multieffect, has attracted attention as a potential alternative for a ring network based on the conventional SONET/SDH (Synchronous Optical Network/Synchronous Digital Hierarchy) devices.
Especially, the packet ring network is attracting high attentions as useful in networks in urban areas. In the IEEE, the work for standardizing the IEEE802.17 RPR, in which standard specifications for a packet ring are put into shape, are now in progress with November, 2003 as a target deadline.
The recent packet ring as described above is generally referred to as an RPR (Resilient Packet Ring) to differentiate it from the token ring or FDDI (Fiber Distributed Data Interface) ring.
The RPR is a network protocol technique mainly provided for an inter-city network (MAN/WAN (Metropolitan Area Network/Wide Area Network)).
The RPR is based on the SRP (Spatial Reuse Protocol) announced by Cisco Systems, Inc., and has the following features:
1. Support for an interactive dual ring network.
2. Support for an MAC (Media Access Control) layer (layer 2)
3. High utilization factor of a used band
4. Plug & Play
5. Capability of switching within 50 ms at occurrence of trouble.
FIG. 35 is a schematic of a conventional RPR network 10. The RPR network 10 includes node devices #a to #f connected to each other to form a duel ring of an inner loop communication path 11i and an outer loop communication path 11o. The inner loop communication path 11i and the outer loop communication path 11o allow bilateral communications in the RPR network 10. Because of the dual ring configuration, even when trouble occurs in one of the rings, communications can be continued via the other ring.
The nodes devices #a to #f are devices for transferring packet data and they function as nodes. The nodes devices #a to #f can be, for instance, a transfer device, a bridge node, a router, server, and any other device dedicated to the RPR.
A packet-based network such as Ethernet typically has the shoe-type or tree-type network. When node redundancy is to be built in the packet-based network as described above, generally the STP (Spanning Tree Protocol) is employed.
Patent document 1: U.S. Pat. No. 6,314,110
Non-patent document 1: IEEE802.17 Draft V2.1
In the conventional technology, when node redundancy is realized with a mesh-formed or a tree-type network, a number of optical fibers are disadvantageously required to be installed anew for connecting the node devices to the redundant node devices.
With the redundant node configuration using the STP, about one minute is required for switching to a bypass route when line trouble or node trouble occurs, and the requirement of telecommunications operators and the like for the high speed switching with the time of 50 milliseconds or below has not been satisfied at all.
Recently, the possibility of RSTP (Rapid Spanning Tree Protocol) developed by improving the STP has been examined, but sill the switching time of several seconds is required even when the RSTP is employed, and the requirement for the switching time of 50 milliseconds or below has not been realized.
The standard RPR (IEEE802.17 draft V2.1) for the conventional type of RPR network does not include any definition on a function for node redundancy. Moreover, the IETF RFC 2892 (The Cisco SRP MAC Layer Protocol) does not include any definition on node redundancy in a ring network.